Fuel tanks configured to store and provide fuel to an engine of a vehicle may be equipped with one or more passive valves. For example, a fuel tank may include a fuel limit vent valve (FLVV), which may comprise a mechanical float valve which can adopt an open configuration when a fuel level in the fuel tank is below a target fuel fill level of the tank, but which may close upon the fuel level reaching or exceeding the target fuel fill level. Such a fuel tank may additionally include two or more grade vent valves (GVVs), which may ensure that the fuel tank is vented at any given incline of the fuel tank. For example, at a particular incline one GVV may passively close to prevent liquid fuel from entering into lines coupling the fuel tank to an evaporative emissions control system, while another GVV may be maintained open to allow communication with the evaporative emissions system, which may prevent buildup of undesired levels of fuel tank pressure.
GVVs may in some examples become stuck in an open state, or a closed state. If a GVV becomes stuck in an open state, then during vehicle accelerations and/or decelerations, liquid fuel may enter into the lines coupling the fuel tank to the evaporative emissions system, and may potentially reach a fuel vapor storage canister positioned in the evaporative emissions system. Such fuel vapor storage canisters may be configured to trap and store fuel tank fuel vapors, before the vapors are purged to the engine for combustion. However, liquid fuel that enters the canister may corrupt the adsorbent material (e.g. activated carbon) therein, which may degrade canister function and which may lead to an increase in the release of undesired evaporative emissions to atmosphere over time. Alternatively, a stuck closed GVV may in some examples result in undesirable pressure buildup in the fuel tank. Accordingly, there is a need to provide onboard diagnostics capable of periodically evaluating whether one or more of the GVVs are degraded (e.g. stuck open or stuck closed), such that mitigating action may be taken to ensure fuel tank integrity is maintained and/or release of undesired amounts of evaporative emissions to atmosphere is reduced or avoided.
The inventors herein have recognized the above-mentioned issues, and have developed systems and methods to address them. In one example, a method comprises predicting an upcoming fuel slosh event in a fuel tank positioned in a fuel system of a vehicle, sealing the fuel system within a threshold duration of the upcoming fuel slosh event, and diagnosing a first or a second grade vent valve coupled to the fuel tank as a function of a fuel level in the fuel tank and a pressure monitored in the fuel system during the fuel slosh event. In this way, fuel tank grade vent valves may be regularly diagnosed as to current operational state, via onboard diagnostics under control of a vehicle controller. Such diagnostics may reduce potential for fuel tank overpressurization events and/or may reduce potential release of undesired evaporative emissions to atmosphere.
As an example, the method may include diagnosing the first grade vent valve under conditions where the fuel level in the fuel tank is lower than a first fuel level threshold but greater than a second fuel level threshold, and may further include diagnosing the second grade vent valve under conditions where the fuel level in the fuel tank is greater than or equal to the first fuel level threshold. In this way, diagnostics for the first grade vent valve and the second grade vent valve may be conducted in such a way as to provide robust results pertaining to whether either the first grade vent valve or the second grade vent valve are functioning as desired or expected.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.